Red phosphorescence compounds

ABSTRACT

Red phosphorescene compounds and organic electro-luminescence device using the same are disclosed. In an organic electroluminescence device including an anode, a hole injecting layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injecting layer, and a cathode serially deposited on one another, the organic electroluminescence device may use a compound as a dopant of the light emitting layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of prior application Ser. No.11/128,421 filed May 13, 2005 now U.S. Pat. No. 7,378,162 whose entiredisclosure is incorporated herein by reference. Further, thisapplication claims the benefit of the Patent Korean Application No.10-2005-0019182, filed on Mar. 8, 2005, which is hereby incorporated byreference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescence device,and more particularly, to red phosphorescene compounds and organicelectroluminescence device using the same. Most particularly, thepresent invention relates to red phosphorescence being used as a dopantof a light emitting layer of an organic electroluminescence device,which is formed by serially depositing an anode, a hole injecting layer,a hole transport layer, a light emitting layer, an electron transportlayer, an electron injecting layer, and a cathode.

2. Discussion of the Related Art

Recently, as the size of display devices is becoming larger, the requestfor flat display devices that occupy lesser space is becoming more indemand. Such flat display devices include organic electroluminescencedevices, which are also referred to as an organic light emitting diode(OLED). Technology of such organic electroluminescence devices is beingdeveloped at a vast rate and various prototypes have already beendisclosed.

The organic electroluminescence device emits light when electric chargeis injected into an organic layer, which is formed between an electroninjecting electrode (cathode) and a hole injecting electrode (anode).More specifically, light is emitted when an electron and a hole form apair and the newly created electron-hole pair decays. The organicelectroluminescence device can be formed on a flexible transparentsubstrate such as plastic. The organic electro-luminescence device canalso be driven under a voltage lower than the voltage required in aplasma display panel or an inorganic electroluminescence (EL) display(i.e., a voltage lower than or equal to 10V). The organicelectroluminescence device is advantageous in that it consumes lessenergy as compared to other display devices and that it providesexcellent color representation. Moreover, since the organic EL devicecan reproduce pictures by using three colors (i.e., green, blue, andred), the organic EL device is widely acknowledged as a next generationcolor display device that can reproduce vivid images.

The process of fabricating such organic electroluminescence (EL) devicewill be described as follows:

-   -   (1) An anode material is coated over a transparent substrate.        Generally, indium tin oxide (ITO) is used as the anode material.    -   (2) A hole injecting layer (HIL) is deposited on the anode        material. The hole injecting layer is formed of a copper        phthalocyanine (CuPc) layer having a thickness of 10 nanometers        (nm) to 30 nanometers (nm).    -   (3) A hole transport layer (HTL) is then deposited. The hole        transport layer is mostly formed of        4,4′-bis[N-(1-naphtyl)-N-phenylamino]-biphenyl (NPB), which is        treated with vacuum evaporation and then coated to have a        thickness of 30 nanometers (nm) to 60 nanometers (nm).    -   (4) Thereafter, an organic light emitting layer is formed. At        this point, a dopant may be added if required. In case of green        emission, the organic light emitting layer is generally formed        of tris(8-hydroxy-quinolate)aluminum (Alq₃) which is vacuum        evaporated to have a thickness of 30 nanometers (nm) to 60        nanometers (nm). And, MQD(N-Methylquinacridone) is used as the        dopant (or impurity).    -   (5) Either an electron transport layer (ETL) and an electron        injecting layer (EIL) are sequentially formed on the organic        emitting layer, or an electron injecting/transport layer is        formed on the organic light emitting layer. In case of green        emission, the Alq₃ of step (4) has excellent electron transport        ability. Therefore, the electron injecting and transport layers        are not necessarily required.    -   (6) Finally, a layer cathode is coated, and a protective layer        is coated over the entire structure.

A light emitting device emitting (or representing) the colors of blue,green, and red, respectively, is decided in accordance with the methodof forming the light emitting layer in the above-described structure. Asthe light emitting material, an exciton is formed by a recombination ofan electron and a hole, which are injected from each of the electrodes.A singlet exciton emits fluorescent light, and a triplet exciton emitsphosphorescene light. The singlet exciton emitting fluorescent light hasa 25% probability of formation, whereas the triplet exciton emittingphosphorescene light has a 75% probability of formation. Therefore, thetriplet exciton provides greater light emitting efficiency as comparedto the singlet exciton. Among such phosphorescene materials, redphosphorescence material may have greater light emitting efficiency thanfluorescent materials. And so, the red phosphorescene material is beingresearched and studied as an important factor for enhancing theefficiency of the organic electroluminescence device.

When using such phosphorescene materials, high light emittingefficiency, high color purity, and extended durability are required.Most particularly, when using red phosphorescene materials, thevisibility decreases as the color purity increases (i.e., the X value ofthe CIE chromacity coordinates becomes larger), thereby causingdifficulty in providing high light emitting efficiency. Accordingly, redphosphorescence material that can provide characteristics of excellentchromacity coordinates (CIE color purity of X=0.65 or more), enhancedlight emitting efficiency, and extended durability needs to bedeveloped.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to red phosphorescencecompounds and an organic electro-luminescence device using the same thatsubstantially obviate one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide an organicelectroluminescence device having high color purity, high brightness,and long durability by combining the compound shown in Formula 1, whichis used as a dopant in a light emitting layer of the organic EL device.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, ared phosphorescence compound is indicated as Formula 1 below:

Herein each of R1, R2, R3, and R4 may be one of substituted ornon-substituted C1 to C6 alkyl groups with disregard of one another.And, each of the C1 to c6 alkyl groups may be selected from a groupconsisting of methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, andt-butyl.

Additionally,

may include 2,4-pentanedione

2,2,6,6,-tetra-methylheptane-3,5-dione

1,3-propanedione

1,3-butanedione

3,5-heptanedione

1,1,1-trifluoro-2,4-pentanedione

1,1,1,5,5,5-hexafluoro-2,4-pentanedione

and 2,2-dimethyl-3,5-hexanedione

Moveover,

may be any one of the following chemical formulas:

Furthermore, the Formula 1 may be any one of the following chemicalformulas:

In another aspect of the present invention, in an organicelectroluminescence device including an anode, a hole injecting layer, ahole transport layer, a light emitting layer, an electron transportlayer, an electron injecting layer, and a cathode serially deposited onone another, the organic electroluminescence device may use any one ofthe above-described formulas as a dopant of the light emitting layer.

Herein, any one of Al and Zn metallic complexes and a carbazolederivative may be used as a host of the light emitting layer, and usageof the dopant may be within the range of 0.1 wt. % to 50 wt. %. Theefficiency of the present invention may be provided when the amount ofdopant used is within the above-described range. Furthermore, a ligandof each of the Al and Zn metallic complexes may include quinolyl,biphenyl, isoquinolyl, phenyl, methylquinolyl, dimethyl-quinolyl,dimethyl-isoquinolyl, and wherein the carbazole derivative may includeCBP.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a graph showing a decrease in visibility as colorpurity of an organic EL device increases (i.e., as the X value ofchromacity coordinates becomes greater); and

FIG. 2 illustrates structural formula of NPB, copper (II) phthalocyanine(CuPc), (bpt)₂Ir(acac), Alq₃, BAlq, and CBP, which are compounds used inembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

A method of combining the red phosphorescence compound according to thepresent invention will now be described. An iridium(III)(2-(3-methylphenyl)-7-methyl-quinolinato-N,C²)(2,4-pentanedionate-0,0) compound, which is shown as A-2 among thered phosphorescene compounds used in the organic EL device according tothe present invention.

COMBINATION EXAMPLE

1. Combination of 2-(3-methylphenyl)-7-methyl-quinoline

3-methyl-phenyl-boric acid (1.3 mmol), 2-chloro-7-methyl-quinoline (1mmol), tetrakis (triphenyl phosphine) palladium(0) (0.05 mmol), andpotassium carbonate (3 mmol) are dissolved in a two-neck round bottomflask containing THF (30 ml) and H₂O (10 ml). The mixture is thenstirred for 24 hours in a bath of 100 degrees Celsius (° C.).Subsequently, when reaction no longer occurs, the THF and toluene arediscarded. The mixture is extracted by using dichloromethane and water,which is then treated with vacuum distillation. Then, after filteringthe mixture with a silica gel column, a solvent is treated with vacuumdistillation. Thereafter, by using dichloromethane and petroleum ether,the mixture is re-crystallized and filtered, thereby yielding solid2-(3-methylphenyl)-7-methyl-quinoline.

2. Formation of chloro-cross-linked dimer Complex

Iridium chloride (1 mmol) and 2-(3-methylphenyl)-7-methyl-quinoline (2.5mmol) are mixed in a 3:1 liquid mixture (30 ml) of 2-ethoxyethanol anddistilled water. Then, the mixture is refluxed for 24 hours. Thereafter,water is added so as to filter the solid form that is produced.Subsequently, the solid form is washed by using methanol and petroleumether, thereby yielding the chloro-cross-linked dimer complex.

3. Formation of iridium (III)(2-(3-methylphenyl)-7-methyl-quinolinato-N,C²)(2,4-pentanedionate-0,0)

A chloro-cross-linked dimer complex (1 mmol), 2,4-pentane dione (3mmol), and Na₂CO₃ (6 mmol) are mixed into 2-ethoxyethanol (30 ml) andrefluxed for 24 hours. The refluxed mixture is then cooled at roomtemperature. Thereafter, distilled water is added to the cooled mixture,which is filtered so as to yield a solid form. Subsequently, the solidform is dissolved in dichloromethane, which is then filtered by usingsilica gel. Afterwards, the dichloromethane is treated with vacuumsuction, and the solid form is washed by using methanol and petroleumether, so as to obtain the chemical compound.

Hereinafter, examples of preferred embodiments will be given to describethe present invention. It will be apparent that the present invention isnot limited only to the proposed embodiments.

EMBODIMENTS 1. First Embodiment

An ITO glass substrate is patterned to have a light emitting area of 3mm×3 mm. Then, the patterned ITO glass substrate is washed.Subsequently, the substrate is mounted on a vacuum chamber. The standardpressure is set to 1×10⁻⁶ torr. Thereafter, layers of organic matter areformed on the ITO substrate in the order of CuPC (200 Å), NPB (400 Å),CBP+(btp)₂Ir(acac)(7%) (200 Å), a hole blocking layer (100 Å), Alq₃ (300Å), LiF (5 Å), and Al (1000 Å).

When forming a hole blocking layer using BAlq, the brightness is equalto 689 cd/m² (8.1 V) at 0.9 mA. At this point, CIE x=0.651, y=0.329.Furthermore, the durability (half of the initial brightness) lasts for1600 hours at 2000 cd/m².

2. Second Embodiment

An ITO glass substrate is patterned to have a light emitting area of 3mm×3 mm. Then, the patterned ITO glass substrate is washed.Subsequently, the substrate is mounted on a vacuum chamber. The standardpressure is set to 1×10⁻⁶ torr. Thereafter, layers of organic matter areformed on the ITO substrate in the order of CuPC (200 Å), NPB (400 Å),BAlq+A-2(7%) (200 Å), Alq₃ (300 Å), LiF (5 Å), and Al (1000 Å).

At 0.9 mA, the brightness is equal to 1448 cd/m² (6.2 V). At this point,CIE x=0.644, y=0.353. Furthermore, the durability (half of the initialbrightness) lasts for 8000 hours at 2000 cd/m².

3. Third Embodiment

An ITO glass substrate is patterned to have a light emitting area of 3mm×3 mm. Then, the patterned ITO glass substrate is washed.Subsequently, the substrate is mounted on a vacuum chamber. The standardpressure is set to 1×10⁻⁶ torr. Thereafter, layers of organic matter areformed on the ITO substrate in the order of CuPC (200 Å), NPB (400 Å),BAlq+A-5(7%) (200 Å), Alq₃ (300 Å), LiF (5 Å), and Al (1000 Å).

At 0.9 mA, the brightness is equal to 1378 cd/m² (6.0 V). At this point,CIE x=0.659, y=0.351. Furthermore, the durability (half of the initialbrightness) lasts for 7000 hours at 2000 cd/m².

COMPARISON EXAMPLE

An ITO glass substrate is patterned to have a light emitting area of 3mm×3 mm. Then, the patterned ITO glass substrate is washed.Subsequently, the substrate is mounted on a vacuum chamber. The standardpressure is set to 1×10⁻⁶ torr. Thereafter, layers of organic matter areformed on the ITO substrate in the order of CuPC (200 Å), NPB (400 Å),BAlq+(btp)₂Ir(acac)(7%) (200 Å), Alq₃ (300 Å), LiF (5 Å), and Al (1000Å).

At 0.9 mA, the brightness is equal to 780 cd/m² (7.5 V). At this point,CIE x=0.659, y=0.329. Furthermore, the durability (half of the initialbrightness) lasts for 2500 hours at 2000 cd/m².

In accordance with the above-described embodiments and comparisonexample, the characteristics of efficiency, chromacity coordinates,brightness, and durability are shown in Table 1 below.

TABLE 1 Durability(h) Current Power ½ of Voltage Current BrightnessEfficiency Efficiency CIE CIE initial Device (V) (mA) (cd/m²) (cd/A) (1m/W) (X) (Y) brightness First 8.1 0.9 690 6.9 2.7 0.651 0.329 1600Embodiment Second 6.2 0.9 1450 14.5 7.3 0.644 0.353 8000 EmbodimentThird 6.0 0.9 1378 13.8 7.2 0.659 0.351 7000 Embodiment Comparison 7.50.9 780 7.8 3.3 0.659 0.329 2500 Example

As shown in Table 1, the device is operated with high efficiency at alow voltage even when the color purity is high. Furthermore, the currentefficiency of the second embodiment has increased by 100% or more ascompared to the comparison example. Additionally, the durability of thesecond embodiment has increased to three times that of the comparisonexample.

Table 2 below shows the characteristics of efficiency, chromacitycoordinates, and brightness in accordance with the increase in voltageand electric current in the organic electroluminescence device accordingto the second embodiment of the present invention.

TABLE 2 Current Power Voltage Current Brightness Efficiency EfficiencyCIE CIE (V) (A(mA/cm²) (cd/m²) (cd/A) (1 m/W) (X) (Y) 5.0 1.111 168.615.2 9.5 0.645 0.353 5.5 3.333 500.8 15.0 8.5 0.645 0.353 6.0 7.777 113914.6 7.6 0.644 0.354 6.5 16.666 2309 13.9 6.6 0.643 0.354 7.0 33.3334275 12.9 5.7 0.643 0.355 7.5 66.666 7664 11.5 4.8 0.641 0.356

As shown in Table 2, the second embodiment provides excellentefficiency, and the chromacity coordinates according to the drivingvoltage also maintains high color purity.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A red phosphorescence compound being indicated as Formula 1 below:

wherein each of R1, R2, R3, and R4 is independently selected from the group consisting of hydrogen and substituted or non-substituted C1 to C6 alkyl groups, and wherein

 represents an alkanedione selected from the group consisting of 2,4-pentanedione, 2,2,6,6,-tetra-methylheptane-3,5-dione, 3,5-heptanedione, 1,1,1-trifluoro-2,4-pentanedione, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, and 2,2-dimethyl-3,5-hexanedione.
 2. The red phosphorescence compound of claim 1, wherein each of the C1 to C6 alkyl groups is selected from a group consisting of methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, and t-butyl.
 3. The red phosphorescence compound of claim 1, wherein

is any one of the following chemical formulas:


4. The red phosphorescence compound of claim 1, wherein the Formula 1 is any one of the following chemical formulas: 